Space planes evenly in an oval
Dupliframes may be a good way for you here 

First, ensure that the origin of your object is placed at the point of the object's mesh which you wish to lie on the curve. To make things easier, align your object so that, untransformed, the local axis you wish to follow the curve is on world Y. (You can change this later, but it's nice not to have to.)

On the plane (or tower) Object Properties > Duplication > check 'Frames'

On the curve, Curve Data > check 'Path animation' and the number of duplicates required in 'Frames', and check 'Follow' if you want the orientation of the duplicates to be tangential to the curve.

Be careful to apply any Object Mode scaling you may have  put on your curve.

Having parented the object to the curve 'Clear its Origin' (AltO, (letter'O')) You can do this at any time, to bring the object's and its duplicates' origins to lie on the curve).

If you need to correct the rotation of the master and its duplicates, with the pivot point set to 'Individual Origins',  rotate the master object around its own pivot point.



I'm confident the object centers are parametrically evenly spaced on the curve - (the tool gives a constant speed in animation) .. but there is a difference in spacing if you use the straight-line approximations to the curve, since, near Y=0 the straight line 'cuts the corner' more than near X=0.